Erythema nodosum what are the causes of this painful lumps in my legs? Since 2008 taking antibiotics twice! And they always come back, why?

Many possibilities. The most common cause is a smoldering infection in teeth, tonsils, bladder, intestine, or elsewhere. Since yours goes away with antibiotic treatment, that's probably what's happening. It is recurring because the infection is recurring - so your doctor needs to run tests to find the exact location of the infection and treat it more specifically. Certain drugs can cause it too, as can other things.